Kevin Macdonald and Ridley Scott's YouTube experiment Life in a Day is a masterfully edited, occasionally moving quilt of user-generated footage from literally thousands of people around the world. It must have started out as a grand idea when the curators sent out a global call via YouTube asking people to submit personal clips shot on 24 July 2010. But the result, which premieres at Sundance film festival tomorrow, is a dissonant art experiment destined to reside on a gigantic wall at Tate Modern.

On paper Life in a Day sounds like an intriguing idea, and Macdonald and his team certainly had their work cut out. That they pulled off the astounding feat of culling a 90-minute documentary from 4,500 hours of footage in the form of around 80,000 clips deserves recognition in itself. But bravura editing and good intentions can't hide the fact is that this fussy but strangely unseasoned dish of exotic ingredients is suffocated by its ambition and ends up being a dollop of visual blancmange.

The first image we see is the majestic rise of a fat, trembling full moon and from there the film proceeds through the cycle of a day. Fauvist splashes are interspersed with the mundane: Ghanaian women sing while they pound grain; an American woman recovering from a double mastectomy talks patiently to her young son; a Russian shoplifter and Parkour expert transforms the city into his playground; an English graduate shares a pint with his dad; Indian men gossip; Ukrainian goatherds herd their goats; Filipino stall-holders eat eggs; girls giggle. It goes on.

We get the picture. We're different but really we're all the same: waking up, going to work, giving birth, talking, laughing, weeping, fighting, coming out, eating, getting drunk, lying, stealing, doing and seeing amazing things, doing and seeing nothing. After about 30 minutes, the film ceases to be engaging and sensory overload diminishes any appetite for the experiment.

All art is manipulative and Macdonald, a keen student of the documentary form who has a list of fantastic credits to his name, can't avoid falling into the trap. He juxtaposes life in developing nations with western consumer trophies such as fancy cars and iPods to convey to us the idea of life's rich (and not so rich) pageant. It feels unnecessary. He returns to certain people so that a smattering of tiny family stories play out within the metanarrative – but why should some be singled out for greater exposure than others?

I'd always been taught that death and taxes are inevitable, so it's strange that they're so lacking in the film, save for footage of the fatal stampede at the Love Parade festival in the German town of Duisburg. And there's no sex. Surely that's inevitable in life, too. This must be what happens when you can rough-hew the world's work to suit your means. At the end of the day Life in a Day ODs on poignancy, and while I commend the optimism and the experiment, I was hoping for a little more tension and vitality.